1. Field of the Invention
The present invention relates to a semiconductor light-emitting device such as an light-emitting diode having a current diffusing layer; and a method for producing the same.
2. Description of the Related Art
In recent years, light-emitting diodes (hereinafter, referred to as "LEDs") have been in the limelight as display devices intended for use indoors and outdoors. Particularly, it is supposed that an outdoor display market will abruptly expand in the years ahead with increase in luminance of LEDs, and LEDs are expected to grow into display media so as to take the place of neon signs in future.
High-intensity LEDs have been realized for a few years in GaAlAs-type LEDs having a double hetero (DH) structure for emitting light in a red-color frequency band for a few years. Moreover, recently, some prototypes of AlGaInP-type LEDs having a DH structure capable of emitting light in the orange-color to green-color frequency bands have been proposed so as to realize high-intensity LEDs.
A portion (a) of FIG. 10 is a cross-sectional view showing a device structure of a conventional AlGaInP-type LED 50 capable of emitting light in the yellow-color frequency band. A portion (b) of FIG. 10 is a diagram showing a carrier concentration profile of each layer of the LED 50. The carrier concentration profile is data obtained from the measurement using a secondary ion mass spectrometer (SIMS), and the absolute value thereof is calibrated by the measurement data for a standard sample.
The LED 50 shown in the portion (a) of FIG. 10 has a multilayered structure formed by sequentially growing, on an n-type GaAs substrate 1 by an MOCVD method, an n-type GaAs buffer layer 10 (thickness: about 0.1 .mu.m, Si doping amount: about 5.times.10.sup.17 cm.sup.-3), an n-type (Al.sub.0.7 Ga.sub.0.3).sub.0.5 In.sub.0.5 P cladding layer 2 (thickness: about 1.0 .mu.m, Si doping amount: about 5.times.10.sup.17 cm.sup.-3), an undoped (Al.sub.0.3 Ga.sub.0.7).sub.0.5 In.sub.0.5 P active layer 3 (thickness: about 0.6 .mu.m), a p-type (Al.sub.0.7 Ga.sub.0.3).sub.0.5 In.sub.0.5 P cladding layer 4 (thickness: about 1.0 .mu.m, Zn doping amount: about 1.times.10.sup.18 cm.sup.-3), a p-type Al.sub.0.7 Ga.sub.0.3 As current diffusing layer 5 (thickness: about 6 .mu.m, Zn doping amount: about 3.times.10.sup.18 cm.sup.-3), and a p-type GaAs cap layer 6 (thickness: about 1 .mu.m, Zn doping amount: about 3.times.10.sup.18 cm.sup.-3). On the underside of the n-type GaAs substrate 1, that is, on the surface opposite to the multilayered structure, an electrode 11 is formed. On the surface of the p-type GaAs cap layer 6, an electrode 12 is formed. In this manner, the LED 50 is constituted.
In the LED 50, a pn junction is formed inside of the active layer 3, and electrons recombine with holes therein so that light is emitted. Intensity of the emitted light is typically about 1.5 candelas when the operating current of about 20 mA is applied.
In the above-mentioned conventional LED 50, the active layer 3 is designed to be an undoped layer. However, in reality, as shown by the carrier concentration profile obtained by a SIMS measurement in the portion (b) of FIG. 10, a p-type dopant (Zn) of the p-cladding layer 4 diffuses into the active layer 3. The diffusion of the p-type dopant degrades crystallinity of the active layer 3, which causes formation of non-radiative centers. As a result, efficiency of light emission of the LED 50 is degraded.